Fuel cell and use of iron-based alloys for the construction of fuel cells

ABSTRACT

A fuel cell is provided which includes iron-based alloys for the construction of the solid parts of the fuel cell. The fuel cell includes a membrane electrode unit and solid constructive parts which may include current collectors, a cell frame and a bipolar plate. At least one of these solid constructive parts is made from an iron-based material that preferably has an effective weight percent of iron of greater than or equal to 26.9 percent.

The invention relates to a fuel cell that comprises a membrane electrodeunit, two current collectors and/or a cell frame or a bipolar plate,whereby at least one solid constructive part is characterized by lowweight and high corrosion resistance of the material used.

BACKGROUND OF THE INVENTION

Up to now, cell frames, bipolar plates, collector plates, and/or othersolid constructive parts of fuel cells, in particular of low-temperaturefuel cells such as the PEM fuel cell, have been known that aremanufactured from graphite or other carbonaceous materials. Thethickness of the plates ranges from at least 2 to 2.5 mm, due to the gasand liquid distribution structure, and, despite the low density of theplate material the plate cause the cells to have a comparatively highweight and large volume.

In EP 0 629 015 Al, the following alloys or metals are disclosed asmaterials for bipolar or collector plates: aluminum, titanium or alloysthereof, zirconium, niobium, tantalum, or alloys of these five elements.In addition, it is there disclosed that these elements can be passivatedby protective electrically insulating oxides, and that, alternatively tothe above-named metals, the plates can also be made of morecorrosion-resistant materials such as graphite, high-alloy stainlesssteel, or nickel-chromium alloys. However, more precise statementsconcerning the composition of well-suited alloys of these metals havenot been known up to now.

For mass production, the carbonaceous materials are too heavy and tooexpensive in the manufacture of cell frames, current collectors and/orbipolar plates, etc. In turn, the metals have an excessively highsusceptibility to corrosion, and, due to their passivation by oxidelayer formation, have excessively high losses during current transportinside the fuel cell.

Therefore there is a need for a fuel cell suitable for mass production,in which the collector plates and/or cell frames and/or otherconstructive parts of the fuel cell are made of a material that

is economical and corrosion-resistant (even in direct contact with theacid membrane electrolytes), and

is easily transformable (good deep-drawing quality), and

has a low contact resistance, and finally

has a low thickness and, above all, a low weight in the processing intoplates, despite the gas and liquid distribution structure.

The subject matter of the invention is a fuel cell that comprises amembrane electrode unit, two current collectors and,or a cell frameand/or a bipolar plate, whereby the material of at least one of thesolid constructive parts is made of an Fe-based material selected fromthe alloys with the following compositions:

C content: 0-0.06 weight % Si content: 0-2 weight % Cr content:8.25-46.5 weight % Mo content: 1.25-14.0 weight % Ni content: 2.25-40.5weight % Cu content: 0-4.0 weight % Mn content: 0-13 weight % N content:0.02-1 weight % Nb content: 0-0.5 weight % P content: 0-0.09 weight % Scontent: 0-0.06 weight % Fe content: remainder to 100 weight %

As an iron-based material, Fe is in principle the main component of theinventively used alloy, whereby the designation main component cannot bedefined by percent indications, but rather is regarded relative to theother components.

Moreover, the subject matter of the present invention is the use of aniron-based alloy with one of the above-named compositions in theconstruction of a fuel cell.

Advantageous constructions of the invention result from the subclaims,as well as from the specification and the examples.

SUMMARY OF THE INVENTION

The Fe-based material for the current collectors and/or the cell frameand/or the bipolar plate is preferably selected from the followingalloys:

C content: 0-0.03 weight % Si content: 0-1 weight % Cr content:16.5-25.0 weight % Mo content: 2.5-7.0 weight % Ni content: 4.5-26.0weight % Cu content: 0-2.0 weight % Mn content: 0-6.5 weight % Ncontent: 0.04-0.5 weight % Nb content: 0-0.25 weight % P content:0-0.045 weight % S content: 0-0.03 weight % Fe content: remainder to 100weight %

Given homogenous alloy element distribution, the relative hole and gapcorrosion resistance of a non-rusting steel can be estimated by means ofthe effective sum (effective sum W=% Cr+3.3. ×% Mo+30 ×% N). In apreferred construction of the invention, the Fe-based material for theat least one solid constructive part is selected of an alloy whoseeffective Sum is ≧26.9, and particularly preferably one whose effectivesum is >30.

In a particularly preferred construction, the Fe-based material isadditionally surface-treated in order to reduce the contact resistance.Gold plating, or also treatment c.g. with titanium nitride, arepossibilities for such surface treatments. However, the surfacetreatment can also be realized by coating with conductive polymerplastics. In principle, all known surface treatments can be used herefor the lowering of the contact resistance with the same or improvedcorrosion resistance.

‘Solid constructive part’ refers here to e.g. cell frames, currentcollectors and/or collector plates, bipolar plates, terminating and/orpole plates, or some other constructive part, such as a frame element,etc., that is usefully constructed from a material whose shape is stableunder normal conditions. These can be square, round, tubular, and otherconstructive parts that can have arbitrary stamped or otherwise formedsurface structures, in which either a cooling medium or a reactionmedium then flows, or into which the membrane electrode unit is alsoclamped. Finally, it can also be a scaling element. In practice, anaxial channel or a tension rod, or a part of an axial channel or of atension rod, can also be made of the inventively used material.

In other words, any additional constriction material of a fuel cell canbe selected from the inventively named alloys, except for the polymerelectrolyte membrane and the two electrodes adjacent to this membrane.

The design in the patent DE 44 42 285 for the construction of a fuelcell provides for the use of production methods suitable for massproduction, such as stamping and pressing, on the materials. Theinventively named Fe-based materials are suitable for Such processingtechniques.

For use as plates with a gas and/or liquid distribution structure, theinventively used Fe-based materials have a small thickness from 20 to300 μm, preferably 50 to 200 μm, and particularly preferablyapproximately 100 μm. For use as pole or terminating plates, or otherapplications, in some circumstances entirely other plate thicknesses areuseful. According to the solid constructive part for which the alloy isused according to the invention, the weight reduction of the fuel cellachieved according to the invention increases naturally with thethickness of the part.

In the fuel cells specified in the above-cited patent, both the poleplates and also the terminal plates and the frame elements can be madefrom the materials, resulting in a considerable reduction in weight inrelation to the prior art.

In the following, the invention is further specified on the basis ofalloys that are preferably used:

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Alloy 1.4539 (material numbers) C content: 0-0.02 weight % Cr content:19.0-21.0 weight % Mo content: 4.0-5.0 weight % Ni content: 24.0-26.0weight % Cu content: 1.0-2.0 weight % N content: 0.04-0.15 weight % Fecontent: remainder to 100 weight % Alloy 1.4462: C content: 0-0.03weight % Cr content: 21.0-23.0 weight % Mo content: 2.5-3.5 weight % Nicontent: 4.5-6.5 weight % N content: 0.08-0.2 weight % Fe content:remainder to 100 weight % Alloy 1.4439: C content: 0-0.03 weight % Crcontent: 16.5-18.5 weight % Mo content: 4.0-5.0 weight % Ni content:12.5-14.5 weight % N content: 0.12-0.22 weight % Fe content: remainderto 100 weight % Alloy 1.4565: C content: 0-0.03 weight % Cr content:23.0-25.0 weight % Mo content: 3.5-4.5 weight % Ni content: 16.0-18.0weight % Mn content: 5.0-6.5 weight % N content: 0.4-0.5 weight % Nbcontent: 0-0.10 weight % Fe content: remainder to 100 weight % Alloy1.4529: C content: 0-0.02 weight % Si content: 0-1 weight % Cr content:19.0-21.0 weight % Mo content: 6.0-7.0 weight % Ni content: 24.0-26.0weight % Cu content: 0.5-1.5 weight % Mn content: 0-2.0 weight % Ncontent: 0.1-0.25 weight % P content: 0-0.03 weight % S content: 0-0.015weight % Fe content: remainder to 100 weight % and alloy 1.3964: Ccontent: 0-0.03 weight % Si content: 0-1 weight % Cr content: 20.0-21.5weight % Mo content: 3.0-3.5 weight % Ni content: 15.0-17.0 weight % Mncontent: 4.0-6.0 weight % N content: 0.2-0.35 weight % Nb content:0-0.25 weight % P content: 0-0.025 weight % S content: 0-0.001 weight %Fe content: remainder to 100 weight %

With the inventively proposed alloys, fuel cells suitable for massproduction can be manufactured economically, and a light and compactconstruction can thereby be realized. In addition, the inventively citedmaterials have a comparatively high resistance to corrosion, even givendirect contact of the plates and/or of the frame elements with the acidelectrolytes. In addition, they have a good deep drawing quality, andare also well able to be transformed. Finally, they have a low contactresistance, which can be further optimized by corresponding surfacetreatment.

From the above description, it is apparent that the objects of thepresent invention have been achieved. While only certain embodimentshave been set forth, alternative embodiments and various modificationswill be apparent from the above description to those skilled in the art.These and other alternatives are considered equivalents and within thespirit and scope of the present invention.

What is claimed is:
 1. A fuel cell comprising a membrane electrode unitand a plurality of solid constructive parts selected from a groupconsisting of a plurality of current collectors, a cell frame, and abipolar plate, at least one of the solid constructive parts comprising aFe-based material comprising the following composition: Cr content:8.25-46.5 weight % Mo content: 1.25-14.0 weight % Ni content: 2.25-40.5weight % N content: 0.02-1 weight % Fe content: remainder to 100 weight%, wherein the Fe-based material comprises an effective sum greater thanor equal to 26.9, and effective sum is defined as Pitting ResistanceEquivalent (PRE).
 2. The fuel cell of claim 1, wherein the Fe-basedmaterial further comprises the following composition: Cr content:16.5-25.0 weight % Mo continent: 2.5-7.0 weight % Ni content: 4.5-26.0weight % N content: 0.04-0.5 weight % Fe content: remainder to 100weight %.
 3. The fuel cell of claim 1, wherein the Fe based materialfurther comprises the following composition: C content: 0.-0.03 weight %Si content: 0-1 weight % Cu content: 0-2.0 weight % Mn content: 0-6.5weight % Nb content: 0-0.25 weight % P content: 0-0.045 weight % Scontent 0-0.03 weight % Fe content: remainder to 100 weight %.
 4. Thefuel cell of claim 1, wherein the Fe-based material is surface treated.5. The fuel cell of claim 1, wherein the fuel cell is a PEM fuel cell.6. A method of constructing a fuel cell comprising solid constructiveparts, the method comprising the step of fabricating the solidconstructive parts from an Fe-based alloy comprising the composition: Crcontent: 8.25-46.5 weight % Mo content: 1.25-14.0 weight % Ni content:2.25-40.5 weight % N content: 0.02-1 weight % Fe content: remainder to100 weight %, wherein the Fe-based material comprises an effective sumgreater than or equal to 26.9, and effective sum is defined as PittingResistance Equivalent (PRE).
 7. The method of claim 6, wherein theFe-based material further comprises the following composition: Crcontent: 16.5-25.0 weight % Mo content: 2.5-7.0 weight % Ni content:4.5-26.0 weight % N content: 0.04-0.5 weight % Fe content: remainder to100 weight %.
 8. The method of claim 6, wherein the Fe-based materialfurther comprises the following composition: C content: 0-0.03 weight %Si content: 0-1 weight % Cu content: 0-2.0 weight % Mn content: 0-6.5weight % Nb content: 0-0.25 weight % P content: 0-0.045 weight % Scontent: 0-0.03 weight % Fe content: remainder to 100 weight %.
 9. Themethod of claim 6, wherein the Fe based material is surface treated. 10.The method of claim 6, wherein the fuel cell is a PEM fuel cell.